Chlorella vulgaris on ceramic tiles as porous substrate bioreactors: Growth kinetics assessment using image processing and scanning electron microscopy

Ceramic-based Porous Substrate Bioreactors (PSBRs) pose a cheaper, less power, and water-intensive alternative to conventional photobioreactors for cultivating microalgae. Current studies do not fully assess the effects of nutrient availability, surface textures, and environmental exposure on microalgae growth in ceramic-based PSBRs. In this investigation, Chlorella vulgaris (C. vulgaris) was cultivated on ceramic tiles characterized by varying surface textures, and exposure to ambient environment, both with and without nutrient medium, and the growth was observed using visible-range imagery. Greenness was monitored using four vegetation indices (VIs). Color parameters (VIs, along with CIELAB color space coordinates (L*, a*, b*)) were used to evaluate the predictive performance of color kinetic models, based on the Root Mean Square Error (RMSE) and Akaike Information Criterion (AIC). Field-Emission Scanning Electron Microscopy (FE-SEM) was used to analyze cellular density, contamination, and surface texture effects on microalgae spatial growth. It was observed that tiles with surface textures yielded better growth than plain tiles. While ceramic could not retain moisture beyond 24 h in an open environment, continuous moisture and nutrient supply supported C. vulgaris growth. Despite contamination by other microorganisms, C. vulgaris proliferated over the tiles provided with nutrient medium. Among the color kinetic models tested, the Exponential model showed better predictive capabilities exhibiting low AIC and RMSE values for 57.14 % of color parameter-surface texture combinations. These findings highlight the potential of ceramic-based PSBRs for outdoor microalgae cultivation with enhanced cellular density due to surface texture and continuous nutrient availability.